Pyridoxal-5'-phosphate (PLP) is the cofactor for a large number of enzymes performing a wide range of biological transformations of amino acids and amines, including transaminations, decarboxylations, and beta- and gamma- eliminations. PLP is capable of performing many of these reactions in the absence of an apoprotein matrix at much lower rates and without regiospecificity and stereospecificity. The goal of our proposed research is to determine the molecular details of the reactions of three PLP- dependent enzymes: l) Tryptophan indole-lyase from E. coli; 2) Tyrosine phenol-lyase from Citrobacter; and 3) Kynureninase from Pseudomonas fluorescens. We are especially interested in studying the role of the protein matrix in providing for the substrate and reaction specificity for these enzymes. These studies will utilize X-ray crystallographic structure determinations, rapid-reaction kinetics measurements, and site-directed mutagenesis of the enzymes.